U.S. patent application number 11/777410 was filed with the patent office on 2008-10-02 for nanomodified concrete additive and high performance cement paste and concrete therefrom.
Invention is credited to Charles L. Beatty, Bjorn Birgisson.
Application Number | 20080242769 11/777410 |
Document ID | / |
Family ID | 38814281 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080242769 |
Kind Code |
A1 |
Birgisson; Bjorn ; et
al. |
October 2, 2008 |
NANOMODIFIED CONCRETE ADDITIVE AND HIGH PERFORMANCE CEMENT PASTE
AND CONCRETE THEREFROM
Abstract
A concrete additive for a reinforced concrete composite is
provided. The additive can have an exfoliated clay having an
exfoliated layered silicate plate comprising structure, and at
least one of an oligomer or polymer linking at least a portion of
said silicate plate comprising structure. The additive can have a
dispersant between the silicate plates. The clay can include sodium
or calcium montmorillonite or a phosphatic clay. The oligomer or
polymer can include polyvinyl alcohol.
Inventors: |
Birgisson; Bjorn;
(Gainesville, FL) ; Beatty; Charles L.;
(Gainesville, FL) |
Correspondence
Address: |
AKERMAN SENTERFITT
P.O. BOX 3188
WEST PALM BEACH
FL
33402-3188
US
|
Family ID: |
38814281 |
Appl. No.: |
11/777410 |
Filed: |
July 13, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60831064 |
Jul 14, 2006 |
|
|
|
Current U.S.
Class: |
524/5 ; 106/819;
524/2 |
Current CPC
Class: |
C04B 28/04 20130101;
C04B 40/0039 20130101; C04B 14/10 20130101; C04B 40/0039 20130101;
C04B 14/104 20130101; C04B 14/104 20130101; C04B 22/124 20130101;
C04B 28/04 20130101; C04B 14/104 20130101; C04B 24/2623 20130101;
C04B 2103/408 20130101; C04B 24/2623 20130101 |
Class at
Publication: |
524/5 ; 524/2;
106/819 |
International
Class: |
C04B 26/02 20060101
C04B026/02; C04B 26/10 20060101 C04B026/10; C04B 14/10 20060101
C04B014/10 |
Claims
1. A reinforced concrete composite, comprising: a cement matrix; an
exfoliated clay having an exfoliated layered silicate plate
comprising structure, and at least one of an oligomer or polymer
linking at least a portion of said silicate plate comprising
structure.
2. The concrete composite of claim 1, wherein said oligomer or
polymer comprises Polyvinyl alcohol (PVA).
3. The concrete composite of claim 2, wherein an average molecular
weight of said PVA is less than 1,000.
4. The concrete composite of claim 1, wherein said oligomer or
polymer comprises 1 to 6 percent by weight of said concrete and
said clay comprises 1 to 5 percent by weight of said concrete.
5. The concrete composite of claim 1, further comprising at least
one dispersing agent.
6. The concrete composite of claim 1, wherein an average spacing of
said silicate plates is at least 4 nm.
7. The concrete composite of claim 1, wherein said cement is
Portland cement.
8. The concrete composite of claim 1, wherein said clay comprises
sodium montmorillonite or a phosphatic clay.
9. A concrete additive, comprising: a stable mixture including: an
exfoliated clay having an exfoliated layered silicate plate
comprising structure, and a dispersant between said silicate
plates.
10. The additive of claim 9, wherein said dispersant comprises
organic ammonium chloride (OAC).
11. The additive of claim 9, further comprising at least one of an
oligomer or polymer linking at least a portion of said silicate
plate comprising structure.
12. The additive of claim 9, wherein an average spacing of said
silicate plates is at least 4 nm.
13. The additive of claim 9, wherein said clay comprises sodium or
calcium montmorillonite or a phosphatic clay.
14. A method of reinforcing a concrete composite, the method
comprising: providing a cement matrix; admixing an exfoliated clay
to the cement matrix, wherein the exfoliated clay has an exfoliated
layered silicate plate comprising structure; and linking at least a
portion of said silicate plate comprising structure using an
oligomer or polymer.
15. The method of claim 14, wherein said oligomer or polymer
comprises Polyvinyl alcohol (PVA).
16. The method of claim 15, wherein an average molecular weight of
said PVA is <1,000.
17. The method of claim 14, wherein said oligomer or polymer
comprises 1 to 6 percent by weight of said concrete composite and
said clay comprises 1 to 5 percent by weight of said concrete
composite.
18. The method of claim 14, wherein an average spacing of said
silicate plates is at least 4 nm.
19. The method of claim 14, wherein said clay comprises sodium
montmorillonite or a phosphatic clay.
20. The method of claim 14, further comprising providing a
dispersant between said silicate plates, wherein said dispersant
comprises organic ammonium chloride (OAC).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application incorporates by reference and claims
priority to U.S. Provisional Patent Application Ser. No. 60/831,064
filed Jul. 14, 2006, entitled "Nanomodified Concrete Additive and
High Performance Cement Paste and Concrete Therefrom."
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
FIELD OF THE INVENTION
[0003] The invention relates to polymer reinforced concretes and
concrete additives.
BACKGROUND
[0004] Conventional concrete, as a construction material, suffers
from a number of inherent deficiencies. The primary drawbacks
relate to its lack of ductility, low tensile strength, and a
tendency to undergo significant shrinkage during curing. The
brittle nature of concrete has had a direct effect on the
specifications and guidelines used in the design of concrete
structures. Since the ultimate goal in the design of any structure
is generally safety, there are a number of precautions that needed
to be taken when formulating the design approaches used today.
Chief among these is the avoidance of brittle failure modes.
[0005] If a structure were to fail in service, people inside that
structure would be at great risk if they had insufficient warning
to vacate the premises before collapse. If such a failure occurred
instantaneously, as in brittle behavior, there would be no warning.
Alternatively, if there was a large amount of deformation, movement
and noise produced by the structure before failure (ductile),
people would have time to get out. Current design codes recognize
this dilemma and base their criteria around ductile failures. The
question becomes how to force a brittle material (concrete) to fail
in a ductile manner.
[0006] The behavior of typical concrete beam to which a uniform
load is added is well known. When the load is applied, the beam
deflects. This causes a shortening of the upper surface of the
beam, resulting in compressive stresses in this region of the
member as the material of the beam (i.e. concrete) tries to resist
the change in shape. The bottom surface, on the other hand, is
lengthened or stretched, resulting in an induced tensile stress as
the concrete tries to resist elongation.
[0007] Concrete is relatively strong in compression but very weak
in tension. If the beam were to be made entirely from concrete, it
would fail at the bottom surface under a very low load, possibly
even its own weight, and that failure would be very brittle in
nature. Thus, something must be done to the lower portion of the
beam to prevent the tensile stresses from failing the concrete.
[0008] This logic is the foundation for conventional reinforced
concrete beam design. Generally, reinforcing bars are placed within
the concrete beam, near the bottom, to carry tensile loads and
alleviate the tensile stresses otherwise applied to the concrete.
Steel, being much stronger than concrete in tension, is well suited
for this application. In addition, steel fails in a very ductile
manner, with very large amounts of elongation before failure. If
this occurs within the concrete, a great deal of deformation and
noise is generated, thus providing the warning necessary to save
lives.
[0009] The basic theory behind conventional reinforced concrete
beam design is well known. Essentially, steel reinforcement is
placed near the bottom of the beam and is used to carry the tensile
stresses while the concrete at the top of the beam carries the
compressive stresses. To avoid failure of this concrete in
compression, the steel is actually under-designed so that it will
fail first. Thus, the concrete never reaches its ultimate
capacity.
[0010] Furthermore, the concrete in the bottom portion of the beam
is not even considered in the design since its strength is very low
in tension, relative to the steel. Its job is simply to protect the
steel from the surrounding environment by acting as a barrier to
deleterious substances (e.g. seawater). Seawater will not
significantly affect the concrete itself but can cause corrosion of
the steel reinforcement, resulting in overall degradation of the
structure. The effectiveness of this approach depends upon the
inherent permeability of the concrete, which is directly dependant
upon the presence and size of cracks. These cracks can and do occur
because of such issues as shrinkage, overloading, fatigue loading,
impact, and other durability mechanisms.
[0011] One method of improving both of these drawbacks (brittle
failure mode, high permeability) is to provide reinforcement of the
concrete matrix at a smaller scale than the steel bars. This is
often done through the use of short fibers mixed into the concrete
during batching. Fibers have the ability to improve durability by
resisting crack opening and provide strength after initial
cracking, thus improving the ductility of the concrete.
[0012] Permeability can also be improved by altering the concrete
microstructure to produce a denser, less porous, arrangement of
components. The most common approach to achieving this goal is the
inclusion of a pozzolanic material in the concrete mix design.
[0013] Concrete is well known to be made up of two primary
components; stone and sand aggregates surrounded by a hydrated
cement paste (hcp) matrix. It is the latter which acts as the glue
that binds the aggregates together. It is also the hcp that is the
dominant factor when it comes to permeability, since the aggregates
typically used in concrete tend to be far less permeable than the
surrounding matrix.
[0014] Examining the hcp matrix reveals that there are two primary
building blocks that make up its microstructure;
calcium-silicate-hydrate (C--S--H) and calcium hydroxide. The
C--S--H takes the form of very small crystals packed closely
together to form a very dense structure. The calcium hydroxide, on
the other hand, forms much larger, layered, plate-like crystals.
These crystals do not pack well and tend to exhibit weakness
between layers due to poor bonding. Ultimately, it is the calcium
hydroxide that represents the weak link in both strength and
permeability of hcp.
[0015] Pozzolanic materials are alumino-siliceous materials which
reacts with calcium hydroxide in the presence of water to form
compounds possessing cementitious properties at room temperature,
producing calcium-silicate-hydrate (C--S--H). The end result is a
significant reduction in porosity and permeability, accompanied by
a corresponding increase in strength. Common pozzolans in use today
include fly ash, silica fume, blast furnace slag, and high
reactivity metakaolin.
[0016] Typical effects of commonly used pozzolanic materials on the
amount of calcium hydroxide in concrete are shown in FIG. 1. The
effect of this reduction in calcium hydroxide on permeability can
be seen in FIG. 2, which shows the relative amounts of chlorides
penetrating into different concretes after prolonged exposed to
seawater.
[0017] Among the large number of clay types available, either
natural or man-made, the polymerization of Montmorillonite (M-clay)
has been the most actively studied. As defined herein and known in
the art "clay" is a term used to describe a group of hydrous
aluminium phyllosilicates minerals that are generally less than 2
.mu.m in diameter that consist of a variety of phyllosilicate
minerals rich in silicon and aluminium oxides and hydroxides which
include variable amounts of structural water. There are three or
four main groups of clays: kaolinite, montmorillonite-smectite,
illite, and chlorite (chlorite is not always considered a part of
the clays and is sometimes classified as a separate group, within
the phyllosilicates). There are about thirty different types of
"pure" clays in these categories but most "natural" clays are
mixtures of these different types, along with other weathered
minerals. Montmorillonite has a chemical formula of
(Na,Ca).sub.0.33(Al,Mg).sub.2Si.sub.4O.sub.10(OH).sub.2.nH.sub.2O.
SUMMARY OF THE INVENTION
[0018] Broadly stated, embodiments of the invention are directed to
a nanomodified concrete additive and high performance cement paste
and concrete made therefrom. A method of making the concrete
composition is also provided.
[0019] The primary chemistry of M-clay can be very similar to
conventionally used pozzolanic materials. M-clay can exhibit a
layered silicate platelet structure. The advantage of this
configuration over other small particles is that the multi-layer
silicate structure can be penetrated between layers by small
molecules forcing the silicate platelets apart (as shown below).
This process is called intercalation. If the penetrating polymer
molecules are reactive species, subsequent polymerization can
result in complete separation of the silicate layers (i.e.
exfoliation).
[0020] As a result of exfoliation, a small mass of M-clay can
result in numerous small, thin (e.g. 20-nm) platelets, with a very
large surface area, that are fully separated. The resulting polymer
chains tends to bond to all of these surfaces, creating a linkage
effect among the silicate platelets. This bonding can also be
considered as a flocculated material since one polymer chain can
link several clay particles together.
[0021] Normally, the exfoliation process requires that the polymer
must wet the clay for it to be able to diffuse into the gallery
(i.e., the spacing between silicate sheet layers). This process can
be slow, and can require mechanical mixing.
[0022] In one embodiment, a reinforced concrete composite is
provided that can have a cement matrix; an exfoliated clay having
an exfoliated layered silicate plate comprising structure, and at
least one of an oligomer or polymer linking at least a portion of
said silicate plate comprising structure.
[0023] In another embodiment, a concrete additive is provided that
can have a stable mixture including: an exfoliated clay having an
exfoliated layered silicate plate comprising structure, and a
dispersant between said silicate plates.
[0024] In yet another embodiment, a method of reinforcing a
concrete composite is provided. The method can include providing a
cement matrix; admixing an exfoliated clay to the cement matrix,
wherein the exfoliated clay has an exfoliated layered silicate
plate comprising structure; and linking at least a portion of said
silicate plate comprising structure using an oligomer or
polymer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] A fuller understanding of the present invention and the
features and benefits thereof will be obtained upon review of the
following detailed description together with the accompanying
drawings, in which:
[0026] FIG. 1 shows typical effects of commonly used pozzolanic
materials on the amount of calcium hydroxide in concrete.
[0027] FIG. 2 shows the effect of various pozzolans on permeability
of hcp.
[0028] FIG. 3 depicts the stress-strain behavior exhibited by the
different mixes during compression testing.
[0029] FIG. 4 shows clay platelets with a gallery therebetween.
[0030] FIG. 5 shows gallery expansion of the platelets of FIG.
4.
[0031] FIG. 6 shows linking of platelets through polymer
chains.
[0032] FIG. 7 is a plot of viscosity in centipoises as a function
of solids content.
[0033] FIG. 8 is a plot of Stress vs strain for concrete samples
with various ingredients after 56 days of curing.
[0034] FIG. 9 is a plot of Stress vs strain for concrete samples
with various ingredients after 56 days of curing.
DETAILED DESCRIPTION
[0035] A reinforced concrete composite can comprise a cement
matrix, an exfoliated clay, and preferably can include an oligomer
or polymer. The oligomer or polymer can link at least a portion of
the exfoliated silicate platelets provided by the clay and can
provide improved ductility and essentially eliminates shrinkage.
The exemplary embodiments of the present disclosure can also be
embodied as a concrete additive, comprising a stable mixture
including an exfoliated clay having an exfoliated layered silicate
comprising structure, and an optional an oligomer or polymer for
linking at least a portion of the silicate comprising
structure.
[0036] Preferred clays for use with the invention include sodium or
calcium montmorillonite (Ex: CLOISITE NA.sup.+) or phosphatic
clays, including phosphatic waste clay, or mixtures thereof.
Optionally, the concrete composite can include a dispersion agent
that helps keep the clay in a dispersed state when stored as an
additive to prevent, or at least limit, clumping of the clay.
[0037] The present disclosure provides polymers or oligomers such
as PVA together with exfoliated clays to form stable admixtures.
When these admixtures are added to a cement matrix form a high
strength, as described below, high ductility concrete results. The
repeat structure of PVA is:
##STR00001##
[0038] PVA in concrete reacts with (OH)-- groups in the cement
matrix, and thus participates in the hydration process forming a
bond with the cement paste. The use of exfoliated clay as a
pozzolan has been found to provide a significant advantage since 2
percent by weight of clay has been found to provide a strength
increase in concrete that is equivalent to about 8 percent by
weight of conventional silica fumes. Moreover, applied to concrete,
the silicate platelets provided by the clay, being pozzolanic in
nature, react with the calcium hydroxide crystals in the concrete
matrix to produce C--S--H, providing all of the associated benefits
(i.e. increased strength, reduced permeability). Additionally,
these new C--S--H crystals form around the polymer chains,
resulting in what is essentially a fiber reinforced concrete,
though the reinforcing is at a scale and consistency never before
achieved. The result of this latter effect is an increase in
ductility of the concrete during failure.
[0039] As used herein, the term "cement matrix" can be a mixture of
a hydratable cementitious binder (e.g., Portland cement), fine
aggregate (sand), and coarse aggregate (crushed stone or gravel) to
which water is added to provide a composition that can harden into
a building structure (e.g., foundation) or a civil engineering
structure (e.g., tunnel) or other structural component.
[0040] The new admixture product for concrete can result in
increased ductility of concrete and reduced shrinkage during
curing. The Inventors have discovered that the intercalation
process can be achieved via time and temperature alone for selected
reactive species on clays including raw ("as dug") M-clay, which is
clay waste produced in phosphate mining (phosphatic clay) as well
as sodium montmorillonite (clay) nanoparticles. M-clay can provide
a plurality of nanosized montmorillonite clay particles.
Introducing a clay together with an oligomer or polymer into the
concrete mixture has been found to produce better contact with the
aggregates leading to better concrete characteristics as there is a
reduction of weak zones between the paste and aggregate.
[0041] As noted above, PVA reacts with hydroxide groups (OH).sup.-
groups in concrete and is thus able to participate in the hydration
process forming a bond with the cement paste. Although the
exemplary embodiments of the present disclosure is described
relative to PVA, other oligomers or polymers, both synthetic and
natural polymers that include functionalities which can react with
hydroxide groups (OH).sup.- groups in concrete and are thus able to
participate in the hydration process forming a bond with the cement
paste, may also be used.
[0042] To further increase obtainable strength and ductility of the
concrete composite an exfoliation process can be applied to the
clay comprising admixture. Exfoliation is a process by which small
particles, such as organic ammonium chloride (OAC) or another
suitable dispersant, and/or the polymer or oligomer molecules can
get into the galleries of the material such as clay and cause it to
expand. If desired, full exfoliation can then be induced through
high shear mixing.
[0043] In one exemplary embodiment for both phosphatic and M-clay,
OAC, and low molecular weight PVA oligomer is added in the
following sequence:
1) OAC is added to the clay. 2a) The mixture is sheared in a high
shear rate mixer (e.g. a Kady mill). 2b) If only clay is used (No
PVA), the solution is then allowed to sit for 24 hours and re-mixed
again at that point in time. This results in an exfoliated clay
system that is ready to participate in the hydration process of
cement paste/concrete in the same way as a typical pozzolan would
(ex: silica fume). 3) If a PVA oligomer or other suitable
oligomer/polymer in the mixture is desired, a low molecular weight
PVA oligomer is added to the exfoliated clay/OAC mixture after step
2a) and the solution is sheared again. 4) The solution is allowed
to sit for 24 hours, after which it is sheared in a high shear rate
mixer again. 5) The resulting solution in now ready for use as an
additive for either regular concrete or cement paste. This results
in an exfoliated clay/PVA oligomer system that is ready to
participate in the hydration process of cement paste/concrete,
resulting in a modified nanostructure with improved ductility and
shrinkage properties.
[0044] The amount of PVA or other suitable oligomer or polymer can
be varied and is generally 1 to 6 percent by weight by total weight
of concrete. The amount of clay can be varied and is generally 1 to
5 percent by weight by total weight of concrete. In one exemplary
embodiment a clay/OAC/PVA solution that consists of a clay/PVA
ratio: 2% clay by total weight of concrete/3 percent PVA by total
weight of concrete.
[0045] The average molecular weight of the oligomeric PVA or other
polymer or oligomer that include functionality which reacts with
hydroxide groups (OH).sup.- groups in concrete is preferably
<1,000, and most preferably <200. Such materials can either
be obtained commercially, or through a supercritical CO.sub.2
processing or other process which functions to reduce the molecular
weight of higher molecular materials.
[0046] The exemplary embodiments of the present disclosure provide
significant advantages, such as enhanced ductility that can enhance
earthquake and blasting resistance. Other advantages can include
minimized pre-mature tensile cracking and temperature
susceptibility. The exemplary embodiments in a foamed product
application can include energy absorbent structures and protective
layers and pre-made panels. The exemplary embodiments of the
present disclosure can provide cost savings and design modification
for building and infrastructure applications of concrete
products.
[0047] The exemplary embodiments of the present disclosure can be
used in a wide variety of products, such as concrete admixtures,
nano-modified ductile Portland cement concrete with aggregates,
nano-modified ductile cement paste, nano-modified ductile energy
absorbent cement foam, such as a spray-on, or pre-batched
application to structural members and structures, infrastructure
and homeland security absorbent products.
[0048] As described above, in one embodiment of the invention
phosphatic waste clay is used to form concrete additives, cement
paste or concrete. Phosphatic waste clay is a by-product generated
by the fertilizer industry when phosphorous is mined. The
phosphatic waste clay is disposed of in settlement ponds, which
require large areas to be taken up. Unfortunately, such ponds
receive acidified leaching during the settlement which is a
recognized as significantly damaging the environment. By using
large quantities of phosphatic waste clay in concrete additives,
cement paste and concrete, the invention will thus materially
enhance the quality of the environment.
EXAMPLES
[0049] It should be understood that the Examples described below
are provided for illustrative purposes only and do not in any way
define the scope of the invention.
[0050] Studies into the utilization of polymer modified clay in
concrete have been conducted. Table 1 below describes the six
different cement paste mixtures tested and provides test results
from compression testing of cylinders.
[0051] The first mix design consisted solely of Portland cement and
water to act as a control mix to which the others could be
compared. Adding the polymer/oligomer (PVA) modifier to the basic
cement paste (Mix #2) resulted in an increased ultimate strain at
failure, but also in a large decrease in strength. Adding only the
clay the control mix (Mix #3), on the other hand, induced a
significant increase in strength and ultimate strain. The former
effect is believed to be a direct result of the pozzolanic reaction
induced by the clay, an effect well known in the concrete
industry.
[0052] Combining both the polymer and clay with the basic cement
paste resulted in very ductile materials, depending upon the ratio
of polymer to clay. A 2:1 ratio (Mix #4) increased the ultimate
strain of the material by over 250%, while a 1:1 ratio (Mix #5)
induced a 344% increase. However, the strength of these mixtures
dropped considerably.
[0053] Upon examining the cement pastes produce in Mixes 4 and 5,
it was discovered that the clay-polymer reaction required a
significant amount of water, which likely resulted in insufficient
water being available for proper cement hydration. Mix #6 was
essentially a repeat of Mix #5, with an increased water content.
The results obtained were unexpectedly highly superior, with the
ultimate strength increasing dramatically while still producing
double the strain exhibited by the control mix.
TABLE-US-00001 TABLE 1 Mixture details and compression testing
results. Ultimate Ultimate Elastic Mix Compounds W/C Strength
Strain Modulus ID Added Ratio (psi) ( ) (ksi) 1 None (Control) 0.45
3100 0.009 583 2 Polymer only 0.43 2500 0.013 287 3 Clay only 0.45
4047 0.011 371 4 Poly & Clay 0.45 360 0.032 22 (2:1) 5 Poly
& Clay 0.45 700 0.040 36 (1:1) 6 Poly & Clay 0.60 2586
0.018 283 (1:1)
[0054] The effect of these additives can be seen even more clearly
in FIG. 3, which depicts the stress-strain behavior exhibited by
the different mixes during compression testing. The black line
represents the control specimens (Mix #1) with neither polymer nor
clay added. The cyan line represents Mix #2 wherein the polymer was
added alone and the navy line shows the pozzolanic effect of the
clay when added alone (Mix #3). All three of these mixes exhibit
the typical concrete failure mode--extremely brittle with virtually
no load carrying ability beyond the ultimate load. Essentially, the
material fails instantaneously. The light and dark purple lines
(Mixes 4 and 5, respectively) show the very large increases in
ductility induced by combining the polymer and clay, though also
show the large decrease in strength.
[0055] Finally, the red line represents Mix #6, the most promising
result. The strength of this mix is nearly as high as the control
and the ultimate strain has been doubled. The most important
feature, however, is the behavior of the material after ultimate
load. Unlike the first three mixes, there is no immediate failure
after the ultimate load is reached. Instead, there is a great deal
of deformation (i.e. strain) after the ultimate load is surpassed
but before the failure load is reached.
[0056] This effect is unheard of in unreinforced concrete and has
the potential to vastly change the design process should the amount
of ductility be increased sufficiently. Additionally, the strain at
which the concrete first cracks, represented by the point at which
the initial linear portion of the curve ends, is much higher than
the control mix. This bodes well for concrete's other job, the
protection of the steel reinforcement. Essentially, a higher
cracking strain would mean fewer cracks in the tension zone of
concrete structural members, which would result in a lower overall
permeability. Ultimately, this means that reinforced concrete
exposed to seawater or other deleterious compounds would last much
longer by protecting the reinforcing steel more effectively.
[0057] Such resistance to cracking will also be extremely
beneficial at early ages to resist cracking due to shrinkage.
Again, the microstructural fiber reinforcement provided by the
polymer chains will carry most of the tensile stresses developed
during shrinkage, thus resisting crack formation and
propagation.
[0058] Exfoliation leads to nanomodification. A tool that aids in
the optimization of both strength and ductility is exfoliation.
Exfoliation is a process by which small particles such as the
organic ammonium chloride (OAC) and the oligomer or polymer
molecules can get into the galleries of a material such as clay and
cause it to expand. In FIG. 4, regular clay platelets are shown
with the gallery between clay layers. In FIG. 5, gallery expansion
occurs due to reactive species.
[0059] Furthermore, the polymer chains help link these expanded
galleries to produce a network through the concrete matrix, thereby
increasing ductility. In FIG. 6, linking of platelets are assisted
by polymer chains.
[0060] When phosphatic clay is used it can have a drawback. It
possesses high water holding capacity due to which the water is not
available for mixing purposes when added to concrete and is thus
known as bound water. Thus, the calculation of bound water in
phosphatic clay is generally required.
Calculation of Bound Water in Phosphatic Clay--Viscosity
Measurements
[0061] The method followed to determine the amount of bound water
is to measure viscosity at various solid concentration levels. At a
particular solid concentration the viscosity rises steeply and the
clay begins to form a solid. It is then that the rest of the water
available is not present for cement hydration. This trapped water
bound by the phosphatic clay should not be a part of the water to
cement ratio. The DVI+Brookfield viscometer is used for the
purpose.
[0062] The table 2 summarizes the viscosity results of samples at
various solid concentration levels in phosphatic clay:
TABLE-US-00002 TABLE 2 Concentration (wt. %) Viscosity (cPoise) 3
1600 25 4000 30 4000 35 10200 37 21000 38 68000 39 70000 40
180000
[0063] It can be seen from the results above and FIG. 7 that at 40%
solid content the viscosity rises steeply. At this stage, there is
no water available and is all bound by the clay. Thus the amount of
bound water for every sample containing phosphatic clay can be
determined using the fact that at 40% of its concentration, no
water is available for mixing. This matter is kept in mind as
concrete samples are made using phosphatic clay.
Step by Step Approach for Mixing Cement Paste Samples with
Phosphatic Clay [0064] 1) Weigh a certain amount of diluted
phosphatic clay sample and dry it overnight to remove the water
from the sample. This will help determine the exact percent of
solids in it. [0065] 2) From the same bucket of diluted phosphatic
clay, take a certain amount of weight in a pan and dry it till it
reaches 15% of solids. Before taking diluted clay from another
bucket, make sure that the exact percent of solids for that bucket
has been determined. [0066] 3) Collect this waste clay at 15%
solids in another bucket till we have a good amount. [0067] 4)
Weigh the correct amounts of cement and water per the mix
requirements. For instance 500 grams of cement is taken for mixing,
with the required water to cement ratio the required water can be
achieved i.e. for 0.6 water to cement ratio, the water required
will be 300 grams. [0068] 5) Now determine the exact amount of clay
substitution required i.e. say if 5% substitution is required
consisting of Clay and PVA (40% clay and 60% PVA in the
substitution) then 25 grams will be required and the amount of
cement required will now be 475 grams. The clay is exfoliated and
mixed/reacted with the PVA before addition to cement paste. [0069]
6) Once this has been established, determine the amount of clay at
15% solids would be required. Like if we require 25 grams of waste
clay, 166.67 grams of waste clay at 15% solids would be required.
[0070] 7) Reduce the amount of water actually required for mixing
by the amount of water obtained from the waste clay at 15% solids
(i.e., 166.67-25=141.67 grams of water is obtained), therefore the
exact amount of water required is 158.33 grams (300-141.67). [0071]
8) With the cement, reduced water and the 15% solids clay solution
we are ready to mix the paste. [0072] 9) The cement is first placed
in the Hobart table top mixer. Then water and the 15% solids clay
mixture are added almost at the same time and the mixer is started.
[0073] 10) The mixture is allowed to mix for 4-5 minutes till
homogeneity is achieved. If the mixture becomes too thick to work
with due to the drop in water to cement ratio, a superplaticizer
called ADVA 100 by GRACE chemicals is added. [0074] 11) The mixture
is then removed and put into the desired cylinders and vibrated on
the vibratory table to help remove voids and help disperse the
paste. This should be performed for at least 2-3 minutes. [0075]
12) The samples are then removed from the cylinders the next day
and put into lime solution for curing. [0076] 13) The samples can
then be tested at their required testing dates according to the
required curing times. Step by Step Procedure for Preparing
Concrete Samples with all Ingredients: [0077] 1) Determine the
water to cement ratio required for the samples to be prepared.
[0078] 2) From the information, using the tables for medium
consistency mixtures in the Portland Cement Association handbook
mounts of cement, water, coarse aggregate and fine aggregate in
pounds per cubic yard which can be converted to the amounts in
kilograms are provided. The maximum aggregate size of the aggregate
used is 3/4''. [0079] 3) Before using this aggregate, it should be
verified that the gradation of the aggregate is in accordance to
the ASTM standards. This is done the same way as for samples with
Cloisite Na+. [0080] 4) Follow steps 1 to 8 for preparing cement
paste samples with phosphatic clay for the achievement of required
amounts of clay and cement by subtracting the amount of clay used
from the amount of cement required. [0081] 5) Before we start
mixing concrete, make sure that we have the required cement, the
required amount of the 5% waste clay mixture, the aggregates and
the remaining water. [0082] 6) First add the coarse aggregate to
the mixer along with the clay mixture in water and the remaining
water. Allow mixing for 2-3 minutes. [0083] 7) Then slowly add the
cement to this mixture followed by the fine aggregate. Allow mixing
for 4-5 minutes till homogeneity is achieved. [0084] 8) Add
measured amounts of super plasticizer if the mix becomes too thick
too handle. The super plasticizer to be used is ADVA 100 from GRACE
chemicals. [0085] 9) Follow steps 11 to 13 from cement paste
samples for completion.
[0086] For both cement paste and concrete samples, the true water
to cement ratio can be calculated using the fact that at 40% solids
content of phosphatic clay, there is no water available for
mixing.
Compression Testing Results of Waste Clay Concrete Samples
[0087] Since the pozzolanic reaction acts to convert CH into
C--S--H, producing a denser matrix and thus increasing strength,
this effect is bound water in phosphatic clay expected to be more
pronounced in concrete than in plain cement paste. Since CH
preferentially forms in areas of high water content during
hydration, and aggregate particles tend to form a film of water at
their surfaces during mixing, CH typically forms along the
interface between the aggregate and the surrounding hydrated cement
paste matrix. It is thus this interfacial zone that ends up being
the "weak link" in the concrete microstructure.
[0088] The fact that the clay acts to convert the CH into C--S--H
means that it should have more effect in concrete because it will
be acting directly on this weakened transition zone, which doesn't
exist in plain cement paste. To prove this theory, a series of
4''.times.8'' concrete samples were made and tested under
displacement controlled compressive loading. Following are the
parameters of the testing: [0089] Displacement rate=0.600 mm/min
[0090] Failure limit=25 mm displacement Testing Results--Exfoliated
Waste Clay with Cloisite Na.sup.+ and Polymer
[0091] As show in the stress-strain data of FIG. 8, the addition of
exfoliated waste clay by itself increases the compressive strength
of samples as compared to regular concrete. There is a noticeable
strength decrease with the addition of polymer and Cloisite
Na.sup.+ with the waste clay. The bounded water with the phosphatic
clay is taken into account for the calculation of water to cement
ratio for samples with the clay.
Testing Results--Exfoliated Waste Clay with Type III Cement and
Polymer for Production of High Strength Concrete
[0092] As show in the stress-strain data of FIG. 9, the addition of
waste clay with type III cement at 56 days yields high strength
concrete. There is a reduction in compressive strength of samples
with the addition of polymer and increasing amounts of waste clay.
But all samples attain a compressive strength of more than 5000
psi, which makes them high strength concrete samples in accordance
to the Portland Cement Association (PCA).
Characterization of Samples--Environmental Scanning Electron
Microscope (ESEM) Pictures
[0093] A scanning electron microscope is essentially an electron
beam based microscope used to examine the surface structure of
prepared specimens. The difference between a regular scanning
electron microscope and an environmental scanning electron
microscope is that the prior needs to be run under vacuum. In
comparison, the environmental scanning electron microscope permits
scanning microscopy at much lower pressures in the presence of a
gas.
[0094] Various images have been recorded for samples with varying
concentrations of ingredients in concrete and the Interfacial
Transition Zone between the paste and the aggregate has been
studied. It was observed that better packing with the aggregate is
observed as compared to a sample with 2% Polymer. It was concluded
that samples with the addition of phosphatic clay and polymer
produce better contact with the aggregate leading to better
concrete characteristics as there is a reduction of weak zones
between the paste and aggregate.
[0095] Other features of the present disclosure are recited in
"Nanomodification of Hydrate Portland Cement Concrete Paste" by
Birgisson et al. and "Summary of Research on the utilization of
nanomodified phosphatic clay" by Birgisson et al., the disclosures
of which are hereby incorporated by reference
[0096] It is to be understood that while the invention has been
described in conjunction with the preferred specific embodiments
thereof, that the foregoing description as well as the examples
which follow are intended to illustrate and not limit the scope of
the invention. Other aspects, advantages and modifications within
the scope of the invention will be apparent to those skilled in the
art to which the invention pertains.
* * * * *